Explain: “Thou who didst waken from his summer dreams ........... All overgrown with azure moss and flowers So sweet, the sense faints picturing them!”

 Explain: 

“Thou who didst waken from his summer dreams

The blue Mediterranean, where he lay,

Lull'd by the coil of his crystalline streams,

Beside a pumice isle in Baiae's bay,

And saw in sleep old palaces and towers

Quivering within the wave's intenser day,

All overgrown with azure moss and flowers

So sweet, the sense faints picturing them!”

Ans: In these lines Shelley describes the effect of the west wind on the sea. In Summer the Mediterranean remains perfectly calm under a blue sky. Hence the poet imagines that it falls asleep, being caught up in the whirling round of its clear and transparent water. Probably in its sleep it dreams of the ruined palaces and towers of the city of Baiae, which once stood on its shore and is now submerged in the sea. These ruins quiver gently when seen through the slight motion of the waves in the Summer weather. They are also overgrown with vegetation and sea-flowers, the fragrance of which is so intense that the senses are overpowered even in imagining it But in Autumn, the west wind rouses the sea from its summer repose and ruffles it with high waves.

These lines give an iridescent picture of the west wind. The poet imaginatively pictures the west wind as rousing the Mediterranean from his summer sleep. In other words, the Mediterranean which remains calm during Summer is terribly agitated when the west wind of Autumn blows through it. 

These lines testify to Shelley's myth-making power. The blue Mediterranean is personified and pictured as a sea-god sleeping and dreaming the whole Summer. He creates myths and relations just as the Greek did.